Studies on Growth, Nitrogen and Energy Metabolism in Rats

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Abstract
Feed intake, growth, nitrogen retention and energy metabolism were measured in 12 male Wistar rats fed ad lib. for 14 weeks with non-purified diets. The feed intake increased rapidly in 4 weeks time from 16 g/d to 25 g/d, and then it was constant in the following 10 weeks. In relation to metabolic live weight the energy intake decreased from about 1400 to 800 kJ GE/kg0.75. With the high intake of energy the growth curve obtained is assumed to be near maximum level. The curve can be transformed to a linear one based on log days expressed as y, LW, g = -836 + 594 X log days with CV = 7.5% and r2 = 0.968. The nitrogen retention increased from 200 to 300 mg N/d in period III when the rats 60 days old, and then it decreased in the following 10 weeks to about 100 mg N/d. In relation to metabolic live weight nitrogen retention is assumed to be near maximum level, decreasing from 1100 to 200 mg N/kg0.75. In the live weight range from 100 to 350 g the total energy retention (RE) increased from about 65 to 125 kJ/d, corresponding to 36% of ME. The energy retained in "protein" increased from 30 to 45 kJ/d, and then it decreased to about 25 kJ/d, while the energy retained in "fat" increased steadily from about 30 to 100 kJ/d in the live weight range from 100 to 350 g. Thereby the ratio between energy retained in "protein" or "fat" decreased from 1:1 to 1:4.
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